Shimano makes two different SPD cleats for MTB-pedals. One that has only lateral play and another one with vertical play as well.
The dual play SM-SH56 type is meant for casual riding and trekking riders who don't feel too secure with tightly clamped shoes and they are mainly used on roads. They unclip with left and right movement and upwards motion. Those might make you feel insecure on a trail because they permit some upward float before unclipping.
The other type SM-SH51 only unclip if you turn the heel sideways, in or out. For both the left and right right freedom is +/- 3°
As other comments pointed out, tightness meaning the point when the pedals releases the cleat is the only possible adjustment. Float is built-in to lessen the load on the knee and cannot be adjusted. This is a road pedal only feature to be achieved with one of three different types of cleats.